As used herein, the following acronyms shall have the following meanings:
3GPP Third Generation Partnership Project
AS Access Stratum
CC Call Control
CM Connection Management
CN Core Network
CS Circuit Switched
eNB e-Node B
EPC Evolved Packet Core
EUTRAN Evolved UTRAN
FDD Frequency Division Duplex
GERAN GSM Edge Radio Access Network
GMM GPRS Mobility Management
GPRS General Packet Radio System
GSM Global System for Mobile Communications
IP Internet Protocol
LLC Logical Link Control
LTE Long Term Evolution
MAC Medium Access Control
MM Mobility Management
MME Mobility Management Entity
MS Mobile Station
MSC Mobile Switching Center
NAS Non-Access Stratum
PDU Packet Data Unit
PS Packet Switched
P-TMSI Packet Temporary Mobile Subscriber Identity
RANAP Radio Access Network Application Part
RLC Radio Link Control
SAE System Architecture Evolution
SA WG System Architecture Work Groups
SGSN Serving GPRS Support Node
SM Session Management
SMS Short Messaging Service
SS Supplementary Services
TDD Time Division Duplex
UE User Equipment
UTRA Universal Terrestrial Radio Access
UTRAN UMTS Terrestrial Radio Access Networks
The Third Generation Partnership Project (3GPP) is a collaboration that was established in December 1998 by the signing of the 3rd Generation Partnership Project Agreement. Third generation systems based on 3GPP specifications rely on the evolution of the so called 2.5 generation Global System for Mobile Communications (GSM) network standards. 3GPP is charged with preparing, approving and maintaining the necessary set of Technical Specifications and Technical Reports for: UMTS Terrestrial Radio Access Networks (UTRAN), including Universal Terrestrial Radio Access (UTRA) (in Frequency Division Duplex (FDD) and in Time Division Duplex (TDD) modes); 3GPP Core Network (capabilities evolved from GSM: include Mobility Management (MM), global roaming, and utilization of relevant Internet Protocols); User Equipment (UE) and terminals for access to the above, and system and service aspects.
The Long Term Evolution (LTE) of the 3G mobile system started in 2004. The initial focus was on the evolution of the UTRA. A set of high level requirements was identified, including reducing the cost per bit, increasing service provisioning, using existing and new frequency bands flexibly, simplifying architecture, using open interfaces and facilitating reasonable terminal power consumption. On certain aspects, the collaboration with 3GPP System Architecture Work Groups (SA WGs) was found to be essential. The split between the Access Network and the Core Network, and the characteristics of the throughput that new services would require demanded close architectural coordination.
A feasibility study on the UTRA and UTRAN LTE was started in December 2004. The objective was to develop a framework for the evolution of the 3GPP radio-access technology leading to a high-data-rate, low-latency and packet-optimized radio-access technology. The study focused on supporting services provided from the Packet Switched (PS) domain, involving, related to the radio-interface physical layer (downlink and uplink), means to support flexible transmission bandwidth up to 20 MHz, introduction of new transmission schemes and advanced multi-antenna technologies and, related to the radio interface layer 2 and 3, signalling optimization. Related to the UTRAN architecture, an objective was to identify the optimum UTRAN network architecture and functional split between RAN nodes.
All RAN WGs participated in the study, with collaboration from SA WG2 in the area of the network architecture. RAN WG3 worked closely with SA WG2 in the definition of the new architecture. The Evolved UTRAN (EUTRAN) consists of e-Node Bs (eNBs), providing the Evolved UTRA user plane and control plane protocol terminations towards the UE. With respect to System Architecture Evolution (SAE), SA WG2 commenced a study for the SAE whose objective was to develop a framework for an evolution or migration of the 3GPP system to a higher-data-rate, lower-latency, packet-optimized system that supports, multiple radio access technologies.
Mobility Management (MM) and Session Management (SM) procedures are conventionally defined for other 3GPP access systems (GSM Edge Radio Access Network/Universal Terrestrial Radio Access Network (GERAN/UTRAN)). However, such procedures have not been defined for LTE/SAE.
Different types of data are passed through an LTE/SAE system. The term signaling is often used to define the type of data that is used to send special control messages that are used to control the system in some manner. The other type of information, the user data, refers to the actual user information that is sent from some source user to a destination user or destination application. In general, the signaling data passes through the control plane. The user data passes through the user plane.
For existing 3GPP systems, the Access Stratum (AS) carries all of the signaling and user data messages that relate to the access technology used across a specific interface in that part of the system. Across the radio interface, the AS protocols are the lower level protocols between the UE and the radio access network, e.g., UTRAN, and between the radio access network. e.g., UTRAN, and the Core Network (CN).
Additionally, at present, the Non-Access Stratum (NAS) carries the signaling messages and user data messages that are independent of the underlying access mechanism. These signaling and user data are passed between the UE and the CN and, conceptually, pass transparently through the radio access network, e.g., UTRAN.
For existing 3GPP systems, the NAS contains procedures for MM for a CS and PS (e.g., General Packet Radio System (GPRS)) as well as CC, SM for GPRS, SMS and SS.
In order to determine the location of the MM and SM procedures in the protocol stack architecture for LTE/SAE, the protocol architecture as defined by SA WG2 must be taken into account. The SAE architecture provides support for packet-switched domain services only. Within the SAE architecture the MME is responsible for the distribution and reception of messages from/to the UE through the eNBs; e.g., paging messages.
It should be noted that UE or terminals which handle communication towards an LTE access system (EUTRAN) and/or existing GERAN, UTRAN would be required, that is 3GPP accesses. As a result, interoperability and mobility between different access networks is a requirement for these UEs and terminals. Further, extensive updates in the UEs or terminals should be avoided since this will, most likely, delay the implementation of SAE. For existing 3GPP systems (such as GERAN, UTRAN), the UE and the core-network, being the Serving GPRS Support Node (SGSN) and Mobile Switching Center (MSC), provide procedures for MM as well as for CC, SM for GPRS (PS domain only), SMS and SS. These procedures are part of the NAS.
There are two different sets of MM procedures specified for CS domain and for PS domain. These two sets of procedures are grouped into two different protocols and handled or managed by different entities.
At present, the MM layer provides support for mobility of UEs, such as informing the network of its present location and providing user identity confidentiality. There are two different entities in the MM layer; the MM entity which handles the protocol (and procedures) for non-GPRS services (CS domain) and the GPRS MM (GMM) entity which handles the protocol (procedures) for GPRS services (PS domain). See 3GPP TS 23.060, 24.007, 24.008.
Examples of the types of signaling messages that are carried via the AS are messages that control the power control loops in the system and handover procedures and that allocate channels to a user for use, for instance in a speech call. An example of an NAS signaling message would be one associated with a call setup request, where the call setup messages are independent of the underlying access mechanism. In this example, the call setup message would come from the CN, and be routed transparently through the AS.
As seen in FIG. 1, the present version of the 3GPP TS 23.401 [2] discloses a UE 101 connected via the LTE-Uu interface 102 to the network (EPC) by two reference points. These are the S1-MME 103, for the control plane, and the S1-U 104 for the user plane. As seen therein, the MME communicates with the existing Serving GPRS Support Node (SGSN) 105. The LTE/SAE architecture provides support only for PS domain services. Hence, to use existing GMM and SM procedures for LTE access systems (such as EUTRAN), requires certain modifications or new procedures. GMM provides three different types of procedures and is located in the network (SGSN) and the UE. These are GMM common procedures, GMM specific procedures and GMM connection management procedures. GMM common procedures are initiated by the network when the UE is registered to the network. These procedures include Packet Temporary Mobile Subscriber Identity (P-TMSI) re-allocation, GPRS authentication and ciphering, GPRS identification and GPRS information. GMM specific procedures are either initiated by the network or the UE. Procedures initiated by the network include: detach the UE for GPRS services and/or non-GPRS services and GPRS detach. Procedures initiated by the UE include GPRS attach, detach, and routing area updating. The GMM connection management procedure is used only when the UE obtains access through a UTRAN. These procedures are initiated by the UE and used to establish a secure connection to the network and/or to request the resource reservation for sending data; service request.
FIG. 2 illustrates the protocol architecture 200 used by between a UE that is capable of communicating over both a CS network and PS network. FIG. 3 illustrates the control plane protocol stack 300 for a mobile station (MS) in communication with a SGSN. FIG. 4 illustrates the conventional control plane protocol stack 400 for a UE in communication with a SGSN.